1. Field of the Invention
The present invention relates to an aerosol-generating apparatus, a film-forming apparatus, and an aerosol-generating method.
2. Description of the Related Art
The aerosol deposition method (hereinafter referred to as “AD method”) is such a technique that material particles, which are converted into an aerosol by being mixed with a carrier gas, are introduced into a reduced pressure space in a film-forming chamber, and the material particles are jetted from a nozzle toward a substrate at a high velocity on the basis of a differential pressure between the internal pressure of the film-forming chamber and the internal pressure of the nozzle so that a coating composed of the material particles is formed on the substrate thereby. In the case of the AD method as described above, for example, when the particle sizes or diameters of the material particles are adjusted to select an appropriate film formation condition, a dense film of the material particles can be formed at a high speed at the normal temperature.
The standard equipment of the film-forming apparatus based on the use of the AD method includes an aerosol-generating apparatus which is capable of forming the aerosol such that the material particles, which are contained in a previously prepared powder, are mixed and dispersed in the carrier gas.
A problem has been hitherto pointed out about the fact that the material particles are aggregated or coagulated and the particle sizes of the material particles are increased when the aerosol-generating apparatus is used for a long period of time. The clusters of the material particles (aggregates of material particles), which are formed by aggregating and solidifying the material particles, tend to stay at a lower portion of the powder accommodated in the aerosol-generating apparatus. Therefore, a particle size distribution arises in the powder such that the particle diameter of the material particle aggregate is increased at lower positions. The aggregates having large particle sizes are gathered in a large amount in the lower layer of the powder. Therefore, the material particles are hardly dispersed in the carrier gas. Any appropriate agitation or stirring function and any appropriate fluidization, which are to be brought about by the carrier gas, are inhibited by the aggregates of the material particles in relation to the entire powder contained in the aerosol-generating apparatus. The aggregation of the material particles is further facilitated. In relation thereto, it is also considered that the agitation state and/or the fluidization state of the powder is adjusted by adjusting, for example, the gas flow rate of the carrier gas. However, whether the gas flow rate of the carrier gas is large or small exerts a serious influence on the coating characteristic of the material particles with which the substrate is to be coated. Therefore, there is obviously a certain limit to suppress the aggregation of the material particles by adjusting the agitation state and/or the fluidization state of the powder by adjusting the flow rate of the carrier gas.
Finally, the material particles, which are disposed at the lower portion of the powder, cannot be converted into the aerosol. Any trouble arises in the long-term stable generation of the aerosol to be brought about by the aerosol-generating apparatus. In other words, in the case of the conventional aerosol-generating apparatus, it is extremely difficult to maintain a constant concentration of the material particles in the aerosol for a long period of time. This fact causes a serious obstacle against the practical use (industrial application) of the film-forming apparatus based on the use of the AD method.
In order to deal with the problem as described above, film-forming apparatuses are disclosed in Japanese Patent Application Laid-open Nos. 2004-113931 and 2004-339565, each of which is provided with a driving means for applying, for example, the minute vibration to an aerosol-generating vessel. For example, in the case of an aerosol-generating apparatus described in Japanese Patent Application Laid-open No. 2004-113931, a predetermined motion can be applied together with the minute vibration to the aerosol-generating vessel in which the aerosol is produced. Therefore, it is affirmed that the aggregates of material particles do not stay without being unevenly distributed at any portion of the vessel, and it is possible to stably produce the aerosol.